There is well known a vehicular electric drive apparatus wherein an electric motor is operatively connected to drive wheels so that the drive wheels are driven by the electric motor. Patent Document 1 discloses an example of such a vehicular electric drive apparatus in the form of an auxiliary drive device 20 of a main drive device 10. The auxiliary drive device 20 of Patent Document 1 is provided with major components including an electric motor 20a, a speed reducing gear train 20b (gear mechanism) for reducing the operating speed of the electric motor 20a, and a differential device 20d. The electric motor 20a is used to drive rear wheels 21b (drive wheels). The electric motor 20a is isolated from the speed reducing gear train 20b by an axle casing 24.